import { IntStart } from './interface';

const maxOrbit = (x:number, y:number) => {
    const max = Math.max(x, y);
    const diameter = Math.round(Math.sqrt(max * max + max * max));
    return diameter / 2;
    //星星移动范围，值越大范围越小，
  }

export const initLoginBg = () =>{
  const windowWidth = document.documentElement.clientWidth || document.body.clientWidth;
  const windowHeight = document.documentElement.clientHeight || document.body.clientHeight;
  // var windowWidth = window.clientWidth;
  // var windowHeight = window.clientHeight;
  const canvas = document.getElementById('canvas') as HTMLCanvasElement;
  const ctx = canvas.getContext('2d') as CanvasRenderingContext2D;
  const w = canvas.width = windowWidth;
  const h = canvas.height = windowHeight;

  const hue = 217;
  const stars: IntStart[] = [];
  let count = 0;
  const maxStars = 5200;//星星数量

  const canvas2 = document.createElement('canvas');
  const ctx2 = canvas2.getContext('2d') as CanvasRenderingContext2D;
  canvas2.width = 100;
  canvas2.height = 100;
  const half = canvas2.width / 2,
  gradient2 = ctx2.createRadialGradient(half, half, 0, half, half, half);
  gradient2.addColorStop(0.025, '#CCC');
  gradient2.addColorStop(0.1, 'hsl(' + hue + ', 61%, 33%)');
  gradient2.addColorStop(0.25, 'hsl(' + hue + ', 64%, 6%)');
  gradient2.addColorStop(1, 'transparent');

  ctx2.fillStyle = gradient2;
  ctx2.beginPath();
  ctx2.arc(half, half, half, 0, Math.PI * 2);
  ctx2.fill();

  // End cache

  function random(min:number, max=0) {
    if (arguments.length < 2) {
      max = min;
      min = 0;
    }

    if (min > max) {
      var hold = max;
      max = min;
      min = hold;
    }

    return Math.floor(Math.random() * (max - min + 1)) + min;
  }

  
  
  var Star = function(this: IntStart) {

    this.orbitRadius = random(maxOrbit(w, h));
    this.radius = random(60, this.orbitRadius) / 18; 
    //星星大小
    this.orbitX = w / 2;
    this.orbitY = h / 2;
    this.timePassed = random(0, maxStars);
    this.speed = random(this.orbitRadius) / 500000; 
    //星星移动速度
    this.alpha = random(2, 10) / 10;

    count++;
    stars[count] = this;
  }

  Star.prototype.draw = function() {
    const x = Math.sin(this.timePassed) * this.orbitRadius + this.orbitX;
    const y = Math.cos(this.timePassed) * this.orbitRadius + this.orbitY;
    const twinkle = random(10);

    if (twinkle === 1 && this.alpha > 0) {
      this.alpha -= 0.05;
    } else if (twinkle === 2 && this.alpha < 1) {
      this.alpha += 0.05;
    }

    ctx.globalAlpha = this.alpha;
    ctx.drawImage(canvas2, x - this.radius / 2, y - this.radius / 2, this.radius, this.radius);
    this.timePassed += this.speed;
  }

  for (var i = 0; i < maxStars; i++) {
    new Star.prototype.constructor();
  }

  function animation() {
    ctx.globalCompositeOperation = 'source-over';
    ctx.globalAlpha = 0.5; //尾巴
    ctx.fillStyle = 'hsla(' + hue + ', 64%, 6%, 2)';
    ctx.fillRect(0, 0, w, h)

    ctx.globalCompositeOperation = 'lighter';
    for (var i = 1, l = stars.length; i < l; i++) {
      stars[i].draw();
    };

    window.requestAnimationFrame(animation);
  }

  animation();
}